Sewage treatment



April 9, 1940. M. T. SINGLETON 2,195,840

SEWAGE TREATMENT I Original Filed Oct. 11, 1935 w 2 Sheets-Sheet 1 SBI Eg h.

0 m 5 m I g INVENTOR. E MICAJAH TSINGLETON 5 m i B) r 1 ATTORNEY.

April 1940- M, T. SINGLETON 2,196,840

SEWAGE TREATMENT Original Filed on.- 11, 1935 2 SheetsSheet 2 on 7 m Flq w p I F 5G. 2. CAI s01 o BP. W3

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WW MICAJAH T. SINGLETON B) VFZ a a q ws IFZ W 6 ATTORNEY.

Patented- Apr. 9, 1940 UNITED STATES SEWAGE TREATMENT Micajah T.Singleton, Atlanta, Ga.

Application October 11, 1935, Serial No. 44,593 Renewed May 17, 1939 8Claims. (oi 210-2) This invention relates to the treating of sewage,trade waste liquors, or other form of impure waters or mixtures thereof.According to one aspect of the invention it particularly pertains toadjusting or insuring an optimum pH value for the most effective andeconomical employment of coagulants or chemicals that are relied uponfor effecting a coagulating, or a precipitating, or a coagulating andprecipitating of in either suspended solids or colloidal matter, or ofboth,- in order to obtain an early elimination or substantial removal ofsuch matter whereby a relatively clear or a relatively clarifiedeflluent is realizedn 15 The present invention, according to an aspectthereof more specifically expressed, revolves about the employment of aC02 bearing gas either as pure CO2 or as a substantial component ofagaseous product-such as any form go of flue gas or other burned gas,engine exhaust gas, incinerator stack gas or sewage digester gas asdirectly produced as the result of sewage sludge digestion or even afterburning or other combustible utilization thereof-for insuring or s 5assisting the pH value to an optimum value below '7, according to whichmany coagulating or precipitating agents can be more economicallyemployed than according to present-day practice. The CO2 bearing gasconstitutes a conditioning 30 agent and accomplishes the desired-end ina rela.-'-

tively automatic manner because it can be employed in. quantitiessufficient to accomplish the desired end, for example to bringthe pHvalue to that at which water will no longer absorb-the 35 CO2, and acontinued excess supply of CO1 will not detrimentally affect the enddesired to be accomplished by its employment.

The present invention .as carried out contemplates the conditioning ofthe sewage, trade 40 waste liquors, or other impure waters, as thecasemay be, by the introduction or mixing therewith or the intimatecontacting therewith of the CO2 bearing gas, thereafter intimatelymixing with the conditioned sewage or other conditioned liq- 5 uid beingtreated the desired or particular chemical. The preconditioning by theapplication or introduction of CO2 bearing gas into the liquid beingtreated is preferably carried out under conditions to lower the pH valueor, as otherwise 50 expressed, to insure-that the'pH value of the liquidbeing treated is within an approximately pH value range of 6.2 to 5.2,.the latterbeing approximately the lowest pH value which can' beeconomically realized. by .the utilization of The pH range mentioned isthat which is favorable to realizing the advantageous features of thepresent invention.

The preconditioning and the chemical application just referred to, oreither of them, is 5 then preferably followed by the employment ofgentle agitative effects favorable to flocculation, that is to theformation or assemblage of the suspended and colloidal matter into theform of flocs, and ultimately by sedimentation, after which thesupernatant liquid is withdrawn as clarified effluent and passes alongone path as to waste or other place of disposal therefor or to place ofutilization thereof while'the sedi-- mented settled solids are withdrawnand suitably disposed of as by digesting or as by dewatering and othersubsequent disposal operation as by burning, to wit incineration;

'linity of a highly alkaline liquid or sludge such as sewage, sewagesludge, trade waste, or other form of liquid bearing organic impurities,to a point at which biological action will take place and proceed at'anoptimum rate, other conditions for optimum operation beingpresent. In-

this connection it is pointed out that in many instances sewage comingin for treatment is frequently heavily loaded with trade wastes whichimpart high alkalinity thereto, and the phase of the invention justreferred to has particularly in view the treating" ofsewages and tradewaste liquors of this type. l

This invention according to one phase thereof 40 7 relates to the use ofcarbon dioxide gas recovered as a by-product ofsewage disposal, eitherfrom the digestergases where sewagesludge'is digested or from stack orflue gases when sludge or screenings are burned, or the use of-COz'produced by the combustion of any fuel or recovered 'from naturalgases, for the purposeof aiding or increasing the eflectiveness ofcoagulation and precipitation of suspended solids or' colloidal matterwhere an acid or an acidic metallic saltis usedas a coagulant and it isfound the effectiveness of such coagulant is'increased by lowering thepH valueof. the sewage and/or yother waste liquid. H

.Where acids such as sulphuric acid or metallic Bl" salts, such asferric chloride, ferric sulphate, chlorinated copperas, aluminumsulphate and other chemical reagents having a strong acid radical areapplied to sewage and/or waste liquids or other impure waters ormixtures thereof, for the purpose of coagulating and precipitating thesuspended solids or colloidal matter or both, the effectiveness of suchtreatment and the quantity of coagulant required for a given degree ofclarification is dependent to a great degree upon the hydrogen-ionconcentration (pH value) of the liquid waste treated. The optimum pHvalue'for most effective and economical coagulation may vary withdifferent coagulants and with the character of the wastes to be treated,but, generally speaking, the coagulants used in the treatment of sewageare more eifective in two different pH rangesone appreciably on thealkaline side of neutrality and the other appreciably on the acid sideof neutrality.

It so happens that municipal sewage is generally approximately neutralor very slightly alkaline, with a pH value of 7.0 to 7.5, being at timesmore acid or alkaline, depending upon the character of the water supplyor nature of industrial wastes present.

While the suspended solids and colloidal matter in sewagecan becoagulated if suflicient quantitles of certain chemicals are applied, itis generally more economical to adjust the pH value either to a pointnear the alkaline optimum by adding lime or other alkaline substance orto a point near the acid optimum by the addition of an acid such assulphuric acid and the like. Such preliminary pH'adjustmen't with acheaper chemical reagent permits of the use of smaller quantities of themore expensive chemical used as the coagulant, and produces betterclarification at less overall expense.

The general trend heretofore, where pH adjustment has been practiced,has been to use lime to raise the pH to approximately 9.0 or higher wheniron salts are used as the coagulant. Equal or better results can berealized in most instances by lowering the pH with acid to 5.5, orlower,

depending upon the particular sewage treated.

The comparative cost of lime or acid treatment is dependent on the localcost of the chemicals used and the character of the sewage beingtreated.

Acid pH adjustment has not met with favor in the past, first: because ofthe fear of damage to plant structures and equiment due to the presenceof sulphuric acid, which is the acid generally used; second: because ofthe fear of the after-precipitation effects when such acid sewage isdischarged into streams; and also because of the more importantdifficulty, namely, that of danger of overdosing with acid at certaintimes because of varying quantities and character of sewage or otherwaste liquid supply due to the fact that the acid is not self-regulatingas to pH value adjustment in the same manner as CO: addition.

This invention as above indicated relates to the introduction of carbondioxide gas in sewage trade waste or other impure water for the purposeof adjusting the pH value thereof by increasing the hydrogen-ionconcentration of the liquid or, otherwise expressed, by lowering the pHvalue for the purpose of effecting a saving in the quantities ofchemicals used as coagulant or for increasing the effectiveness of suchcoagulants when coagulants are applied to sewage and/or otherwasteliquids for the purpose of precipitating suspended solids orcolloidal .matter.

The pH value adjustment effected by C02 is caused not only by thereduction of hydroxides to bicarbonates but further by the directionization of the carbonic acid formed by the excess CO2 introduced. Theacid resulting from the introduction of CO2 in the water of the sewageis a weak acid andwill not damage structures or equipment, if reasonableprotective measures are practiced, and therefore a C02 bearing gasbecomes a feasible and practicable adjusting agent or reagent.

The invention possesses other objects, aspects and features ofadvantage, some of which with the foregoing will be set forth in thefollowing description. In the following description and in the claims,parts will be identified by specific names for convenience, but they areintended to be as generic in their application to similar parts as theart will permit. In the accompanying drawings there have beenillustrated the best embodiments of the invention known to me, butsuchembodiments are to be regarded as typical only of many possibleembodiments, and the invention is not to be limited thereto.

The novel features considered characteristic of my invention are setforth with particularity in the appended claims. The invention itself,however, both, as to its organization and its method of operation,together with additional objects and advantages thereof, will best beunderstood from the following description of a specific embodiment whenread in connection with the accompanying drawings in which Figure 1diagrammatically illustrates a relatively complete sewage treatingsystem clearly indicating the modes and location of using a C02 bearinggas prior to the sedimenting or settling out of chemically precipitatedor chemically coagulated solids, and in this figure there are indicatedcertain modes of obtaining the CO2 bearing gas employed, any one ofwhich modes can be used alone or all of which can be simultaneouslyemployed.

Figure 2 diagrammatically illustrates a simplified arrangement thatemploys certain of the fundamental arrangements that exist in that ofFigure 1. It will be noted in the arrangement of this Figure 2 thatsettled sludge derived from the sedimentation or settling 'out of thechemically precipitated or chemically coagulated solids is passed to adigester from which the combustible gas resulting from the digester isdirectly employed as a C02 bearinggas or is utilized ina gas engine orother gas utilizing unit the exhaust or outflow gaseous product of.whichis employed as a C02 bearing gas.

Figure 3 diagrammatically illustrates a simplifled arrangement thatemploys certain of the fundamental arrangements that exist in that ofFigure 1. It will be noted that according to Figure 3 the sludgeobtained as the result of settling out chemically precipitated orchemically coagulated solids is passed to a mechanical filter fordewatering, thereafter the dewatered sludge is burned in an incineratorand a stack gas resulting from such burning is utilized to provide theCO2 bearing gas that is employed in the process.

Figure 4 is a diagrammatic view illustrating an arrangement according towhich an alkaline type of sewage is obtained andwhich is reduced as toits alkalinity by C02 bearing gas preparatory to realization ofoxidation effects, as by an activated sludge process or by a tricklingfilter oper- 2,196,840 ation that is followed by clarification prior toof the sludge into the digester.

The drawings will now be described in detail. For ready reference,certain designating characters are listed below. They indicate certainapparatus, parts or devices employed in the systems illustrated andwhich are useful for treating sewage or the like. The parts indicatedthereby are referred to elsewhere in the specification.

The members or parts designated have in general the characteristicsindicated.

AT designates an aeration tank or device wherein sewage or sewage sludgecan be activated due to the introduction or mixing therewith of air, forexample air which is blown into and delivered from perforated pipes orthe like within the tank.

BP designates a bypass arrangement by which a certain part or section ofthe sewage treating system is bypassed or, as otherwise expressed,

BP designates an arrangement employed for obtaining a split flow for theliquid as it passes along a particular section of the system.

C designates an apparatus wherein a sedimentation operation. is carriedout, such apparatus being frequently referred to as a clarifler.

CA designates a coagulating agent supply and generally it is a chemicalor other material functioning to effect the coagulating or precipitatingof coagulable material in the liquid and of the fine and/ or colloidalsolids suspended in the liquid undergoing treatment.

F designates apparatus wherein a liquid that has been chemically treatedor that has been otherwise rendered in condition favorable to flocformation is subjected to gentle but positive agitation or agitativeeffects carried out in a manner favorable to the formation or productionof fines. Certain chemical apparatus for accomplishing the agitativeeffects above referred to is sold under the trade name Flocculator. The

word floc as employed herein is equivalent to 4 the sludge itself orfrom fuel derived from an outside source as well as from the sludgebeing incinerated.

M designates an apparatus or device for intimately contacting or mixinga particular ingredient with liquid such as a C02 bearing gas in certaininstances or as a coagulating agent in other instances.

P designates a pump suitable for use in causing or insuring a flow ofeither gas or liquid, as the case maybe, in the proper direction asrequired. RC- designates a certain return conduit arrangement foreffecting a return or recirculation of settled sludge or of a certainefliuent liquid portion, as the case may be, from a certain section ofthe treating system to a preceding section thereof.

SB designates a sludge drying bed upon which sludge is received anddried by exposure to the atmosphere.

SD designates a sludge digester in which sewage sludge is anaerobicallydigested.

TF designates a trickling filter, to wit a construction according to theoperation'of which sewage sludge or the like is distributed over the topof a bed of assembled conglomerate material provided as by a bedcomposed of broken rocks, and allowed to trickle downwardly through theinterstices in the presence of air and jelly-like bacterial orbiological forms existing in the bed. According to the broader aspectsof certain phases of this invention the trickling filter and itsfunctioning may be viewed as illustrative of any suitable means or modesby which aerobic biologicalor oxidizing steps are realized.

V designates adjustable closure members as valves or shut-off gateswhich are employed in various pipes or conduits of the system.

VF designates a vacuum filter or other equivalent type of a mechanicaldewatering device, to wit a device which can be relied upon foreffecting a mechanical elimination or filtering of a substantial portionof the liquid component of sewage sludge and, for the purpose indicated,it'is contemplated that a type of machine. known as a centrifuge may beemployed in and for the accomplishing of the mechanical dewatering.

W designates a pipe line or conduit leading to a locality away from theparticular arrangement shown.

,X designates a source of chemical which will aid or further bacterialaction on a trickling filter or other biological sewage treatment deviceemployed in the system. I

The above reference characters are generally used in conjunction with areference numeral in order to facilitate direct reference to aparticular member, part or device.

' Each of the arrangements illustrated can be employed in the treatingof raw sewage, settled sewage, sewage sludge, trade waste liquid or,liquors, or mixtures of the foregoing, and such may be referred to andincluded by the more general expression liquids undergoing treatment."

Arrangement-of Figure 1 The arrangement-shown in this figure isrelatively complete and affords opportunity for various modes ofoperation according to particular requirements or according to thewishes of a particular operator. It will be appreciated that itsometimes becomes advisable to change the operation of a treating plantof the type involved to take care of different conditions eitherseasonal, periodic, or otherwise, respecting the incoming liquid to betreated.

The incoming liquid enters along the path i and passes into the mixer Mlwherein a C02 bearing gas is brought into intimate contact therewith. Anacid coagulant passes from the source of supply CAI either directly intothe mixer Ml through the pipe 3 or into the line 5 V through the pipe 4,according to whether valve V3 or V4 is open. Bypass BPl can beemployedto obtain a split fiow part of which may be through the mixer MI andpart of which may be through the bypass BPl to the line 5. The CO2bearing gas effects the desired pH value adjustment in the mixer MI andthe acid coagulant provides the coagulating and precipitating agent andbecomes intimately mixed with the liquids thus treated thereby. The thustreated liquid is sometimes referred to as a chemically dosed liquid andit passes into the fiocculator Fl. Within the fiocculator Fl a gentleagitative effect is carried out which is conducive to a fioc formation.

By use of bypass BPI, for example, a split fiow can be obtainedaccording to which sewage can be highly carbonated in MI and thereaftercan be applied to or mixed with incoming sewage from the main fiow assupplied through the bypass BPl. The acid coagulant which is added fromthe source of supply CAI just referred to may be a ferric chlorideFeCla, a ferric sulphate Fez(SO4)3, chlorinated copperas FeCl.SO4, oralum A1z(SO4)3. It will be noted that each of the acid coagulants justmentioned come under the broad classification of chemical reagentshaving strong acid radicals and in fact they represent reagents in whicha strong acid radical is associated with a metallic element of highvalence. From Fl the fiocculated liquid passes along the path 6 into theclarifier Cl The supernatant liquid from the clarifier passes along thepath 1 into the mixer M2, thence along the path 8 into the tricklingfilter TFl The settled sludge obtained by the sedimentation in theclarifier Cl passes therefrom along to path it. The handling of thissludge will be later referred to. Iron salts as from source X may beintroduced into the mixer M2 wherein it is intimately contacted with theliquid undergoing treatment, and this is prior to the distribution ofthe liquid over the trickling filter TFI. The bypass BB2 permits thecomplete bypassing of the mixer M2 if desired, or it can be employed toprovide a split flow part of which passes through the mixer M2 and partthrough the bypass BP2. The iron salt may be a ferrous salt FeSO4 or anyof the ferric salts previously mentioned and may be added for thepurpose of aiding the biological action on the trickling filter. On thetrickling filter TFl bacterial or biological action takes place as theliquid trickles downwardly through the interstices of the bed of thefilter in the presence of air, and the eflluent from the tricklingfilter passes along the path 9 into the mixer M3. It will be borne inmind that a trickling filter when properly functioning has a jell-likegrowth which functions in the realizing of the desired bacterial orbiological process referred to. An acid coagulant can be supplied to theliquid from the source of supply CA2 through the branch l4 or l5dependent upon whether valve Vlfl or W5 is open. In this way the liquidfrom the trickling filter becomes chemically dosed prior to entering thefiocculator F2 in which it is subjected to gentle but positive agitationof a character which aids or furthers the fioc formation. A bypass BP3is provided which, according to desire, can be relied upon for effectinga split flow, part of which will be through the mixer M3 and part ofwhich will be through the bypass BP3, or if desired the bypass BP3 canbe relied upon for completely bypassing the mixer M-3. The liquid fromF2 passes along a path ll into the second clarifier C2 wherein it issubjected to a second sedimentation. The supernatant liquid then passesas eflluent from the clarifier along the path l2 into a mixer M4, thencealong the path l3 to W, to wit to a locality outside the treatingapparatus. The mixer M4 may be employed to intimately contact air withthe liquid passing therethrough so as to eliminate certain of the highCO2 acidity efiects and to avoid subsequent settling orafter-precipitation which might otherwise follow. Bypass BP4 may berelied upon for completely bypassing the mixer M4 and for a directdelivery of the liquid to the outside locality W. Settled sludge, ifreturned into the system, can be relied upon to aid floc formation andalso to physically aid in settling suspended solids, and in thisconnection a return conduit construction RC is provided with suitablevalves therein according to which settled sludge from the clarifier C2can pass along the path 20 for introduction by RCl into the line aheadof the fiocculator Fl, by RC2 into the line ahead of the clarifier Cl,and by RC3 into the line ahead of fiocculator F2. The return to thepoints indicated may of course be to the desires of a particularoperator.

In the operation of a plant or system such as herein outlined, it isadvisable to have bypass arrangements for each of the several operatingunits whereby any one or more thereof can be either temporarilyeliminated or partially by passed for either a long or a short periodaccording to the desires of a particular operator or according tooperative requirements which may arise, and to that end other bypassarrangements are provided by such members as BP5, BPB, BPI, BPB and BPS.With proper valves open it will be noted that liquid can be bypassedfrom the incoming line l through BP5, thence through BPS into line I, orthrough BP'l into line 9, or BP8 into line ll, or BPB into line l3.Likewise liquid can be passed from line 1 through BPS and thereafterthrough BPl into line 9, BPB into line It, or BPS into line l3. BPlpermits the passage of liquid from line 9 through BPB into line H andBPS into line l3, while BPB permits the passage of liquid from line llthrough BPS into line l3. Of course the operations just describedcontemplate the adjustment of the proper valves V for accomplishing thedesired results.

The sludge from clarifier Cl is passed therefrom along path l6 by branchl6 leading to digester SDI or by branch ll into vacuum filter VFl Sludgefrom the clarifier C2 can pass therefrom with the proper valves openalong the paths 20, 2|, 22 and 23 into the line l4 and from the latterby branch It or by branch ll as the case may be into the digester SDI orinto the vacuum filter VFl or into both the digester and the filter. Inthe digester the sludge is subjected to anaerobic digestion with theresulting production of a combustible gas bearing some 002, andtherefrom the gas can pass directly to the gas engine or gas burner GE lor it can be bypassed by BPlll into the line l8 from which there is adirect connection through a valve controlled branch to M3, or throughanother valve controlled branch to Ml. The gas from the digester is of acharacter which will operate a gas engine or gas burner and the exhaustfrom the gas engine or burner is conducted so that it ultimately reachesthe line H! referred to, whereby the exhaust gas from this engine orburner can be utilized if desired as a C02 bearing gas.

Means are provided for conductingovertlow liquor from the digester in amanner whereby it is returned to the system at a locality ahead of themixer Ml. Means are also provided so that the sludge from the digestercan be withdrawn therefrom in a manner to pass some or all of thewithdrawn sludge into the vacuum filter after conditioning withchemicals at CA3, or so that some or all of the withdrawn sludge canpass to the sludge drying bed or beds SBI. Part or all of the dewateredsolids obtained from the filter operation are passed to waste or arepassed into the incinerating furnace IF wherein it is burned, and thestack gases resulting from this burning operation are conducted to thepipe line l8 previously referred to and this provides another source ofCO2 bearing gas which can be employed in either the mixer Ml or. themixer M3. The line 18 has a pipe or section leading to W2, also ifdesired another pipe or section leading to W3, which, when open, allowsa bleeding of CO2 bearing gas to waste. Other forms of CO2 hearing gasmight be employed such as gas obtained as the result of burning coke,and a supply for such forms of CO2 bearing gas other than thosedescribed as obtained from the sewage solids is indicated by GS! and isconnected by suitable piping to the line I 8 previously referred to.Means are provided for conducting filtered liquid from the filter VFI tothe head of the system, namely into pipe I.

It is to be noted that in the arrangement of this figure an activatedsludge system may be substituted in place of the trickling filter TFI.The similarity of the activated sludge system and the trickling filterTFI is that by each, aerobic bacterial oxidation is carried out and thebacterial aid supplied from X to the mixer M2 is helpful in realizingthe desired bacterial effects.

Where chemical precipitation is employed in combination with biologicaltreatment, such as by applying the chemically treated sewage toactivated sludge treatment, trickling filter and the like, this processhas particular application. Alkaline pH adjustment or extremely acid pHadjustment is apt to have inhibitive eflfects upon such bacterialaction. The use of carbon dioxide gas for the purpose of reducing thechemical coagulant required may result in free CO2 becoming entrained inthe liquid undergoing treatment, and it is hereby pointed out thatacidity due to such free or entrained CO2 will be more quickly andreadily overcome by the aeration or oxidizing which is' a natural partof the activated sludge treatment or of the functioning of the tricklingfilter. In such instances the pH value is raised to a point which 'wouldbe the optimum range for the bacterial action.

After coagulation and sedimentation as carried out for example in M3, F2and C2, a very short period of aeration as in M3 will serve to free theclarified liquid of the excess CO2 and raise the pH value, thuspreventing after-precipitation eifects.

Arrangement of Figure 2 Figure 2 is an arrangement which can be embodiedin a relatively simple form of plant. According to the arrangement inthis figure, the incoming liquid fiows along the path I into the mixerMl, thence along the path 5 into the fiocculator Fl, thence along thepath 6 into clarifier Cl from which the efliuent passes along the path Ito W which may be a locality outside of the treating system. The acidcoagulating agent may be introduced into the mixer MI or into the path 5just prior to the introduction of the liquid into the fiocculator. TheCO2 bearing-gas is obtained as the result of passing the sludge from theclarifier into the digester SDI from which the digester gas can bepassed directly into the mixer or to W3, a locality outside of thesystem, if desired. Also according to this arrangement, if desired, thegas from the digester can be utilized in the gas engine or gas burnerGEI from which the exhaust gas can be passed into the mixer Ml or to W3,all of this according to the desires of a particular operator. It willbe noted that the arrangement of this Figure 2 is practically a simpleembodiment of a sub-section of the arrangement of Figure 1.

Arrangement of Figure 3 This illustratesanother simple form embodyingcertain aspects of the invention. According to the arrangement of thisFigure 3, the incoming liquid passes along the path I into the mixer Ml,thence along the path 5 to fiocculator Fl. The liquid undergoingtreatment has an acid coagulant supplied thereto either in the mixer Ml'or in the line 5 ahead of the flocculator, An arrangement is madewhereby the C02 bearing gas can be used as a pH value adjusting agent,the same as is true in the arrangement of Figures 1 and 2. FlocculatorFl functions to aid in the forming of fiocs as desired, and therefromthe fiocculated liquid passes along the path 6 into the clarifier Clfr'omwhich the clarified eiiluent passes along the path I to W and alsofrom which the settled solids pass as sludge into the filter VFI. Thedewatered sludge passed from the filter VFI into the incineratingfurnace IF and the stack gases therefrom are conducted as desired to themixer Ml for use as a pH value adjusting agent, or to W3 which may be alocality outside of the system.

Arrangement of Figure 4 According to the arrangement of this figure, CO2bearing gas is employed as a pH value adjusting agent ahead of anoperation in which the sewage, trade waste or other impure liquid, issubjected to an oxidizing effect. According to the arrangement of thisfigure, the incoming liquid enters the mixer M5 wherein a chemicaldosing agent is added such as lime from asource X and an acidcoagulating agent such as has been mentioned from source Y, andtherefrom the liquid passes to a fiocculator F3. A bypass BPI2 isprovided leading from the line ahead of M5 to the line leaving F3. Theliquid passes-from F3 into the clarifier C3 wherein it is subjected to asedimentation operation. The supernatant liquid passes as effluent fromthe clarifier C3 into the mixer M6, thence along a pathway having. onebranch leading to an activated sludge aerating tank AT, and a branchleading to a trickling filter TF2.. In AT the liquid is activated due tothe introduction of air and therefrom the activated liquid passes intoclarifler C4. From the trickling filter TF2 the liquid is subjected tothe usual bacteriological and biological processes in the presence ofair as an oxidizing agent. The eifluent from the trickling filterultimately passes to bearing gas. Inthis way a desired pH adjustment isrealized. According to the operation of the arrangement shown in thisfigure it may be necessary only to bring the liquid undergoing treatmentdown to a pH value which is approximately 7 or even below that figure.

The arrangement of the parts shown in this figure is such that, ifdesired, sludge can be passed from the underflow of C3 into the lineleading to F3. The underflow or sedimented solids from C4 can be passedto the digester SD! or to the vacuum filter VFZ. The sludge or underfiowfrom either C4 or C5 or both can likewise be passed to either the sludgedigester SDZ or to the vacuum filter VF2. The overflow from the sludgedigester can be passed to the line leading to \the clarifier orsedimentation apparatus C3.

Settled solids can be passed from the sludge digester SD2 either to thesludge beds SR2 or to the vacuum filter VF2. From the sludge bed 832either the liquid passing therefrom, if there is any, or the solidsremoved therefrom, if there are any removed, can be passed to W, alocality outside of the system, or such liquid as may pass from thesludge bed can be passed along and into the line leading to theclarifier C3. Gas from the digester SD! can be passed either to the gasengine or gas burner GE! from which the exhaust gas passes into the linel8, or the gas from the digester can be caused to flow througha bypassBP|3 leading directly to the line l8. This line l8 may be considered asa common line for receiving and transporting any CO2 bearing gas to themixer M6. The sludges which are passed to the vacuum filter VF2 aredewatered therein. The dewatered sludge can be disposed of by passingalong the path leading to W5 which is a locality exterior of the system,or along a path leading to IF2 wherein the dewatered sludge is burned,from which a solid ash residue is passed to locality W6 which is outsidethe system. The

efiluent from the filter VFZ is returned to the system ahead of theclarifier C3. The stack gases or products of combustion are passed fromthe incinerator IF2 along a path leading to the line l8 heretoforereferred to, or along a. path leading to a locality which is exterior ofthe system, to wit, a locality W'l. An outside source of CO2 bearing gasis indicated at GS! and this supply is connected by a line leading toline I 8 heretofore referred to.

Arrangement of Figure 5 According to the arrangement of this figure,sewage enters along a path leading to clarifier C6 and flows into said'clarifier wherein it is subjected to sedimentation. From the clarifierthe eflluent passes to W8. The settled sludge is passed from theclarifier to the mixer M where it is subjected to a pH value adjustmentbecause of C02 bearing gas that is brought into intimate contact withthe sludge as the mixer functions. From the mixer the CO2 treated sewageis passed to the sewage sludge digester SD3 wherein it is subjected toanaerobic digestion. The digester gas, or at least some of it, is passedfrom the digester to the mixer M wherein it is utilized to provide theC02 required. Any digester gas not required for this operation. can bepassed to W9. The eiiluent from the digester is passed therefrom backinto the system. ahead of the clarifier.

Solids remaining as the result of the digestion operation are passedfrom the digester to will.

The'fiow sheet or arrangement of this figure is useful in the handlingof a sludge obtained in the clarifier C6 that has high alkalinitybecause of the fact that the sewage entering the clarifier was highlyalkaline. The passing of the alkaline sludge through the mixer andtherein intimately contacting the sludge with the CO: and the digestergas, reduces or overcomes the high alkalinity so that by the treatmentin the mixture the pH value is lowered to about pH! preparatory to theintroduction into the digester wherein anaerobic digestion takes place.

The following general remarks are in order as aiding in bringing outcertain features that are within the scope and purview of the invention.

CO2 can be generated by burning coke, oil or other fuel, or, in somecases, can be'obtained from natural gas wells or even from the burningof the settled solids after they have been substantially dewatered, oreven from the combustible gas realized by the digestion of sewagesludge. The carbon dioxide (CO2) either in a pure state or diluted withother gases or as obtained as an ingredient or component of a C02bearing gas, can be introduced into the sewage or other liquid byblowing it under pressure through submerged jets, perforated pipes,grids, porous plates or porous tubes, or by the use of a gas absorptiontower through which a part of the sewage can be pumped and the gasintroduced counter-currently. Tests indicate that it is best to applythe CO2 before the coagulant but the CO2 can be applied simultaneouslyor after the coagulant.

According to present-day practices the solid matter precipitated fromthe sewage is generally settled in clarifier tanks as sludge and removedto separate digestion tanks by mechanical means or is settled into thelower digestion chamber of two-story sedimentation and digestion tanks.The settled sludge thenundergoes decomposition .or digestion throughanaerobic bacterial action.

The gas given oi! as a product of such digestion usually amounts toabout 1 cu. ft. per day per capita connected to the sewer. This gas isabout 30% carbon dioxide. The remaining 70% of the digested gas islargely methane.

In carrying out the process of the present in vention according to anarrangement in which a sludge digester SD is employed, there results adigester gas having chemical characteristics above indicated. It willtherefore be appreciated that the digester gas of the arrangement showncan be directly employed as a C02 bearing gas that is suitable for thecarrying out of the present invention. Sewage sludge digester gas iscombustible and since carbon dioxide is a. product of combustion, themethane can be burned and the flue gases from the burner used as anadded source of carbon dioxide. According to the present invention thedigester gases can be first passed through the sewage to utilize the CO:in the natural gas, the methane can then be'recovered and burned forheating purposes or used in internal combustion engines for generatingpower. For whatever purpose the gases are used,

the flue gases or exhaust gasesare a source of constituting impuritiestherein, the method which comprises mixing with the liquids beingtreated a closing chemical reagent having a strong acid radical forcoagulating and'precipitating a substantial portion of coagulatablesecond sedimentation, withdrawing the supernatant liquid of the secondsedimentation along one path and the settled sludge of the second,sedimentation along another path.

2. In the treating of sewage, the method which comprises lowering the pHvalue of incomin sewage by intimately contacting therewith CO2 bearinggas, thereafter mixing therewith as a dosing chemical .a reagent havinga strong acid radical which is employed for coagulating andprecipitating certain of the organic matter in the incoming sewage,subjecting the thus dosed sewage to sedimentation for effecting apreclarification step, withdrawing the settled solids along one path andthe supernatant liquid-along another path, further dosing the withdrawnsupernatant liquid with an acid metallic salt and exposing said treatedliquid to a biological action in the presence of an oxidizing gas,withdrawing the liquid and certain solid products of said biologicalaction and subjecting the same to a second sedimentation for effecting afurther clarification step, and passing the supernatant liquid from saidsecond sedimentation along one path and the settled solids along anotherpath.

3. In the treating of sewage, trade wastes, impure waters and likeliquids having organic matter constituting impurities therein, themethod which comprises intimately contacting a C02 bearing gas with theliquid in a manner whereby the CO2 bearing gas operates as a pH valueadjusting agent, thereafter exposing the liquid 1 which still has some.organic matter therein to biological action in the presence of anoxidizing atmosphere, subjecting the biologically acted upon liquids tosedimentation, and withdrawing the supernatant liquid of saidsedimentation along one path and the settled sludge thereof alonganother path.

4. In the treating of sewage, tradewastes, impure waters and likeliquids having organic matter constituting impurities therein, themethod which comprises subjecting the liquid to an initial sedimentationoperation, withdrawing supernatant liquid along one path and sedimentedsludge along another path, intimately contacting a CO: bearing gas withthe withdrawn supernatant in a manner whereby the C0: bearing gasoperates as a pH value adjusting agent, thereafter exposing thewithdrawn supernatant liquid which still has some organic matter thereinto biological action in the presence of an oxidizing atmosphere,subjecting the biologically acted upon supernatant liquid to a secondsedimentation, withdrawing the supernatant liquid of the secondsedimentation along one path and the settled sludge of the secondsedimentation along another path.

5. In the treating of sewage, trade wastes, impure waters and likeliquids having organic matter constituting impurities therein, themethod .which comprises mixing with the liquids being.

treated a chemical reagent for coagulating and precipitating asubstantial portion of the coagulatable organic matter, separatingcoagulated organic matter from the liquid thereafter, intimatelycontacting a C02 bearing gas with the liquid in a manner whereby the CO2bearing gas operates as a pH value adjusting agent, subsequentlyexposing the liquid which still has some organic matter therein tobiological action in the presence of an oxidizing atmosphere, subjectinthe biologically acted upon liquid to sedimentation, withdrawing thesupernatant liquid-of said sedimentation along one path, and passing thesettled sludge of said sedimentation along an-- other path.

6. In the treating of sewage and other impure 'liquids having organicimpurities therein, the method which comprises lowering the pH value of.incoming liquid by intimately contacting therewith CO2 bearing gas,thereafter subjecting the liquid to sedimentation for effecting apreclariflcation step, withdrawing the settled solids along one path,passing the supernatant liquid along another path and exposing it tobiological action in the presence of an oxidizing gas, withdrawing theliquid and certain solid products of said biological action andsubjecting the same to a second sedimentation for effecting a furtherclarification step, passing the supernatant liquid from said secondsedimentation along one path, and passing the settled solids alonganother path.

'7. In the treating of sewage, trade wastes, im-

. pure waters and like liquids having organic matter constitutingimpurities therein, the method which comprises intimately contacting aCO: bearing gas with the liquid being treated in a manner whereby theCO2 bearing gas operates as a pH value adjusting agent, thereaftermixing a chemical reagent having a strong acid radical, subsequentlyexposing the liquid to biological action in the presence of an oxidizingatmosphere. subjecting the biologically acted'upon liquid to asedimentation, and withdrawing the supernatant liquid of saidsedimentation alongone path and the settled sludge along another path.

8. In the treating of sewageand analogous im pure liquids, the methodwhich comprises lowering the pH value of incoming liquid by intimatelycontacting therewith CO2 bearing gas, thereafter subjecting the liquidto sedimentation for effecting a ore-clarification step, withdrawing thesettled solids along one path and the supernatant liquid along anotherpath, dosing the withdrawn supernatant liquid with an acid metallicsalt, exposing said dosed supernatant liquid to a biological action inthe presence of an-oxidizing gas, withdrawing the liquid and certainsolid products of said biological action and subjecting the same to asecond sedimentation for effecting a further clarification step, passingthe supernatant liquid from said second sedimentation along one path andpassing the settled solids from said second sedimentation along anotherp th.

' MICAJAH T. summon.

